1. Field of the Invention
The present invention relates to surgical methods and devices to stabilize vertebra, and more particularly to plates and rods anchored by cables for immobilizing human spine vertebrae.
2. Description of Related Art
Degenerative disc disease accounts for more than 100,000 low back spinal fusion procedures in the United States annually, according to Columbia, Colo. hospitals. The intervertebral disc is a pad of cartilage-type material situated between spinal bones. Each disc serves as a connector, spacer, and shock absorber for the spine. A soft, jelly-like center is contained by outer layers of fibrous tissue. Healthy discs help allow normal turning and bending. Trauma or injury to the spine can cause discs to tear, bulge, herniate, and even rupture. This can be quite painful, as the soft center of the disc leaks, putting pressure on the adjacent nerve roots and spinal cord.
A damaged disc can cause nerve dysfunction and debilitating pain in the back, legs and arms. Typical treatments that provide relief and allow patients to function again include back braces, medical treatment, physical therapy and surgery to remove the disc. A conventional surgical solution removes the bad disc and promotes new bone growth in the space to fuse the adjacent vertebrae together.
One conventional approach implants one or more metal rods to bridge across a damaged portion of the spine. Such rods lock the bridged-over spinal vertebrae so they cannot twist or flex on their intervertebral discs. In some cases, such discs may have been removed and the object of the spinal fixation is to promote bone growth that fuses the vertebrae together. Such a system is described by Erik Wagner, et al., in U.S. Pat. No. 5,989,250, issued Nov. 23, 1999. Bone hooks and bone screws secured to individual vertebrae serve as anchors for a bridging spinal-rod. The rods are dressed to follow along the lamina inside the two parallel canals formed by the posterior spinous processes of each vertebrae. A similar system is described by Robert Howland in U.S. Pat. No. 5,030,220, issued Jul. 9, 1991.
DePuy AcroMed, a subsidiary of Johnson & Johnson, markets several spinal-fixation systems and devices. For example, the ISOLA Spinal System is a rod-based, thoracic and lumbar multi-level fixation system. Dr. Kiyoshi Kaneda's Anterior Spine Stabilization System is another that is universally used for tumor and trauma spinal fixation. The ACROMED Cable System by Matthew Songer, MD, uses multi-strand cable for cervical, thoracic and lumbar fixation. The ACROPLATE Anterior Cervical System uses a titanium plate on the cervical anterior, and is secured with bi-cortial screws.
Edward Benzel, et al., describe a spinal column retainer in U.S. Pat. No. 5,800,433, issued Sep. 1, 1998. A pair of parallel fenestrated support rods are secured to each vertebrae with a middle plate. A number of holes in each plate allow bone screws to be used to secure the plate to the respective vertebrae. Such plates do not span between vertebrae, the rods do that. Set screws in the plates allow the plates to be locked to each rod, and thus will resist twisting and/or sliding.
Erik Wagner, et al., also describe in U.S. Pat. No. 6,030,389, issued Feb. 29, 2000, a bone plate device for human spine stabilization. Such plates are anchored with bone screws that are angled to one another so that they will bed deeply into the strongest bone material.
A direct rod-to-bone attachment screw is described by Robert Songer, et al., in U.S. Pat. No. 5,662,653, issued Sep. 2, 1997. A bone screw resembling an eye-bolt is screwed into the vertebrae and fenestrated support rod is threaded through the eye-loops. Clamps in the eye-loops open to receive the rods and lock them within.
All such bone screw dependent systems suffer from screw breakout and screw backout problems. Various ingenious techniques and devices have been developed to mitigate these problems, but cable-anchored approaches seem to be superior.
Some prior-art spinal-fixation systems pass loops of heavy cable or wire under the spinal lamina and through the spinal canal. This, of course, must be done without disturbing the nerves or spinal cord. There is a little spare room in the spinal canal not required by the spinal cord. Each thoracic vertebrae in the back, for example, has a vertebral canal with a small space in the posterior (dorsal) corner, adjacent to the lamina. There a cable can be safely passed through. But just forward of this is the spinal cord which is very delicate and absolutely cannot tolerate being squeezed or disturbed.
A surgical cable system and method is described by Erik Wagner, et al., in U.S. Pat. No. 6,053,921, issued Apr. 25, 2000. A metal crimp or collet is used to secure a cable in a loop. A tensioning device allows the cable to be tightened around vertebral bone.
The anchor wires of prior art spinal-fixation systems are conventionally twisted around opposite ends and the fenestrated support rods. Such can easily slip and twist on the usually smooth rods. The alternative anchor cables are multi-strand wires that cannot simply be twisted together. Various cable clamps and locks have been marketed commercially to secure such cables to the rods. A bone-banding cable is described by Leo Whiteside, et al., in U.S. Pat. No. 5,772,663, issued Jun. 30, 1998.
Once a cable has been passed, a device can be used to secure the cables like that described by Robert J. Songer, et al., in U.S. Pat. No. 5,116,340, issued May 26, 1992. Surgical cables looped through spinal vertebrae are conventionally secured by Songer crimping pliers.
All the United States Patents cited herein are incorporated by reference. Such Patents themselves cite many prior art patents and technical documents that will assist the reader in understanding and implementing embodiments of the present invention. These are lodged in the file wrappers of those Patents.
What is needed is a spinal-fixation system that combines thoracic and lumbar posterior plates or bars anchored with cables or wires that individually pass through the spinal canals of adjacent vertebrae.